This invention relates to an improved filter element adapted for clarifying and purifying large volumes of fluid, preferably water. Although the primary use of the filter of the invention is in swimming pool systems it will be apparent to those skilled in the art from the following description that the invention is not so limited, and may also be utilized in any other fluid system having an open or upressurized reservoir.
To maintain the cleanliness and clarity of swimming pool water water circulation systems containing a filter often employing sand or diatomaceous earth as the filtration medium are utilized. The flow of water passes through such filter and contaminants are gradually removed through recirculation. However, it has been found that in some instances the removal of algae and fine particulate matter is not sufficiently accomplished through the use of sand filters, and often requires other mechanical or chemical means to facilitate their removal.
To facilitate such removal through the use of a filtration material an extremely fine pore size is required and this requirement is not always met through the use of sand. It is, however, met through the use of a boundary type filtration material having fine pores formed of impregnated paper a plastic or other filtration material, such as porous metal, woven wire mesh and the like, all of which are well known in the art.
It was suggested in U.S. Pat. No. 2,792,943 to Macintosh that a conventional sand or diatomaceous earth swimming pool filter can be replaced with a porous cloth bag having a sufficiently small pore size to permit the removal of common swimming pool contaminants. Macintosh discloses that his proposed filtration bag can be disposed directly within the swimming pool and that flow by means of a recirculation pump can be directed through the porous material from the inside of the bag, thus eliminating the need for a housing to enclose the filter. While in theory, this concept appears advantageous, in practical use the Mackintosh filter tends to become plugged with contaminants from the pool after a very short period of use due to the lack of sufficient filter area, and would thereupon require cleaning or replacement. This creates an inconvenient situation, since a swimming pool recirculation system for maximum efficiency must be kept operating on a regular basis without the need for frequent maintenance. It follows, therefore, that in order to utilize the concept of a barrier filter disclosed within a swimming pool as set forth in the Mackintosh patent, a different type of filter must be utilized which would provide longer life and yet maintain the fine particle removal rating necessary for a swimming pool application.
The prior art teaches that increased area in a filter can be accomplished by pleating or corrugating the filtration medium and arranging the same in a cylindrical configuration. Examples of such filters can be found in U.S. Pat. Nos. 4,108,775 to Wilkes et al., 4,046,697 to Briggs et al. and 3,376,979 to Bair. However, although the filters disclosed in each of these patents can be produced with a relatively large filtration area, it can be seen in each instance that the flow is adapted to proceed from the outside of the filter to the inside, and thus the use of these filters requires a housing as is shown in Wilkes et al. If the filters of Briggs et al. or Bair were used as a replacement fo the Mackintosh bag after a short period of use as the filter material became plugged and the differential pressure thereacross increased due to the restricted flow, the pleated filter material would tend to expand and ultimately would burst, thus releasing the contaminants contained on the inside to the pool water. In both the Bair and in Briggs et al. patents the filters disclosed include an outer tubular member, however, the structures shown have insufficient strength to restrain the filter material against a high internal pressure and thus could not be utilized as suggested.